The present invention relates to hoses and more particularly to flexible metal hoses that are constructed from helically wound metal ribbons that have interlocked, hermetic convolutions.
Flexible metal conduits made from thin sheet metal ribbons which are convoluted and joined at their edges have been constructed in the past. So-called xe2x80x9cinterlockedxe2x80x9d conduit is a relatively commonplace example. Interlocked conduit employed thin metal ribbons wound helically with their convolutions secured together by reversely curved ribbon edges which were interlocked. The interlocked edges permitted limited play between adjacent convolutions so the conduit could be flexed. U.S. Pat. No. 4,197,728, issued Apr. 15, 1980, discloses a conduit constructed in this manner.
Interlocked metal conduits were, and remain, in widespread use and perform in a generally satisfactory way. In some applications however, these conduits have had inadequate flexibility, convolutions have separated when too much bending was experienced, and the interlocked joints themselves have not exhibited adequate hoop strength. These deficiencies have been primarily limited to applications where relatively thin walled fairly large diameter conduits are specified.
Other flexible metal conduit constructions have been proposed in which flexibility is gained primarily by the manner of formation of the conduit convolutions. U.S. Pat. No. 4,486,484 issued Dec. 4, 1984, discloses such a conduit formed from convoluted metal ribbon which is corrugated. In this construction the helical corrugations provide flexibility while the joint between the convolutions is relatively inflexible. Other corrugated convoluted conduits have been proposed in which the convolution joints are tightly crimped but these have drawbacks related to the joint strength, the joint flexibility and/or the ability of the conduit material to form the joint.
One such conduit is disclosed by U.S. Pat. No. 5,158,814, issued Oct. 27, 1992. That conduit was particularly useful as a chimney flue because it could be flexed to avoid obstructions when installed in a building structure and the junctures of its convolutions were hermetic so that flue gases did not escape into the building. The convolution interlocking structure was formed by ribbon edge flanges that were rolled together to form a multiply hollow bead that extended along and immediately adjacent a corrugation at the convolution junctures. The hose appeared to be formed with a double corrugation running helically along its length because the bead was approximately the same size as the corrugation. The bead and immediately adjacent corrugation combined to substantially stiffen the conduit in the vicinity of the convolution juncture. Even though the remaining corrugations were flexible and enabled flexing the conduit somewhat during installation, the helically extending bead interlock structure, adjacent a corrugation, stiffened the conduit and therefore limited its use. This excessive stiffness was particularly troublesome in building flue applications where the such conduits had to be flexed in order to route them around obstructions The present invention provides a new and improved flexible metal conduit wherein the convolution junctures are formed as part of a regular corrugation and the convolution interlock structure does not reduce the conduit flexibility in the vicinity of the convolution junctures.
A flexible metal conduit constructed according to a disclosed embodiment of the invention comprises a thin metal ribbon arranged in a helix about a longitudinal axis. Convolutions of the helix are disposed adjacent each other with the ribbon defining helical, sinuously corrugated inwardly and outwardly facing conduit surfaces forming radially inner and radially outer apices that are spaced substantially evenly apart and extend helically along the conduit. A first ribbon edge region is defined by a partial corrugation and a flange extending radially from the partial corrugation. A second ribbon edge region is defined by a second partial corrugation and a second flange extending radially from the second partial corrugation. The first and second partial corrugations abut to form a helical seam running along the convolution junctures in an otherwise substantially continuous corrugation on one conduit surface. The first and second edge flanges abut at the composite corrugation seam and are interlocked adjacent the other conduit surface to secure the convolutions together.
In the disclosed embodiment the flanges are tightly rolled together to form a bead-like structure having a generally circular cross sectional shape. The first and second partial corrugations form a single corrugation having a radially inner apex, with the flanges interlocked radially outwardly from the radially inner apex. The disclosed conduit has edge flanges that abut at the radially inner apex of the composite corrugation formed by the first and second partial corrugations. The flanges are interlocked to form a bead-like locking structure that is disposed radially outwardly from the radially inner apex of the composite corrugation.
Other features and advantages of the invention will become apparent from the following detailed description of a preferred embodiment made with reference to the accompanying drawings.